NTSB Issues Directive on Using Deice Boots

Use them early and often; that’s the message from the NTSB when it comes to activating deicing boots on your aircraft. The longstanding debate over so-called “ice-bridging” notwithstanding, the safety board recommends inflating the boots with as little as one-quarter inch of ice on the surface. Those who subscribe to the ice bridging theory believe that activating the boots too early will leave a ridge of ice buildup just aft of the boots, causing more harm to the aerodynamics than good. In a report issued last week, the NTSB writes: “The Safety Board has no known cases where ice bridging has caused an incident or accident, and has investigated numerous incidents and accidents involving delayed activation of deice boots. Ice bridging is extremely rare, if it exists at all.” According to the report, accumulation of as little as one-quarter inch can increase stall speeds by as much as 40 knots-but that the deterioration could be inconsistent from one occurrence to the next: “The danger is that some one-quarter-inch accumulations have minimum impact, and pilots become overconfident.”